The cleaning system is the “digestive system” of the combine harvester, which is the core working section that significantly affects the quality, efficiency and adaptability of the entire apparatus. Most of the larger rice combine harvesters in China use a traditional wind-sieve cleaning system (single-channel centrifugal fan+double-layer vibrating screen). A single-channel centrifugal fan is used to produce clear air, using the difference in suspension velocity among grains, short straws, chaff and small amount of miscellaneous fines, etc.), combine with a double-layer vibrating weaving sieve or fish scale sieve to complete the separation of the grains and straws, and the miscellaneous fines, etc. As a practical matter traditional wind sieve cleaning section design is the main limiting factor to the development of large-scale rice combine harvesters in China. A specific manifestation is that the water content of high-yield super rice is high, and the floating rate of each component is staggered. It is difficult to quickly separate the grains, which seriously restricts the performance and efficiency of the cleaning system. The traditional cleaning system cannot adapt to improvements of crop varieties, and rapid increases in yield requirements.
Large and medium-sized combine harvesters such as the 988 STS (John Deere), the 2388 (CASE), the CR980 (New Holland) and the TUCANO 470 (CLAAS) have been developed in recent years, by John Deere, CASE, New Holland, CLAAS and other manufacturers. However, such large and medium-sized combine harvesters are mainly used for harvesting wheat, soybean, rape and other dry crops, since such large and medium-sized combine harvesters which may have a length of over 6-10 m, and a dead weight were about 8-10 tons cannot adapt to China's southern super-rice producing areas which typically are of 10-15 acres of plot size and present a deep mud angle operating environment. In addition, a conventional cleaning system using a double fan (or large diameter double duct fan), a pre-selected jitter plate (with a corrugated surface), a return conveyor plate (with a corrugated surface), a multi-layer screening screen and other composite structure, used with large and medium-sized combine harvesters cannot be applied to China's rice combine harvesters. So-called “half-size” combine harvesters made by Japanese and South Korean companies have their own limitations, cannot achieve large-scale, operational efficiency and harvest adaptability. Moreover, although Europe and the United States and other developed countries produce large-scale combine harvesters, their relevant test data, design theory and methods are maintained as trade secrets. In short, there is no relevant theory and method that can be used to guide the designing of China's large-scale feeding rice harvesters and its cleaning system, and because of the specific characteristics of the operating conditions in China, we cannot borrow foreign product design experience.
In addition, due to the significant differences in the working conditions of a combine harvester, operating conditions are ever-changing and the operating environment is extremely complicated, the performance of the cleaning system is significantly affected. The structure and motion parameters of the conventional cleaning system can only be carried out by manual adjustment, the working parameters cannot be adjusted based on the objects and the environment changes automatically to ensure top working performance, and harvesting adaptability is poor. To maximize performance, operating parameters need to be adjusted according to conditions to adjust for trends of technological development. For advanced combine harvesters, electronic information technology has been widely used, with joint harvesting function according to operational processes of the work automatically adjusting for various operating parameters, while improving the production efficiency, and controlling failure rate, while greatly improving the machine's trouble-free working hours. Compared with advanced combine harvesters of European and American multinational companies, China's grain combine harvesters are mostly equipped with only a small number of alarm devices, and general lack of working parameters and operating performance monitoring, working parameters such as electric/automatic adjustment and other intelligent monitoring device, result in machine operating performance being unstable, operating efficiency mainly depending on the skill level of the machine operator, and the handling of large, plug the fault frequently, the trouble-free working time less than one-fifth of foreign models, cannot meet the scale of China's rice production and rice oil (wheat) rotation area harvest and other operating requirements. In recent years, domestic and foreign scholars have done a lot of research work on intelligent technology of combine harvesters, but most of the research is only a research on the monitoring or prediction model of single working parameters and operating performance parameters, and not based on the current operation. Parameter value of the relevant parts of the feedback control and multi-operation parameters of the fusion control research is relatively small.
In addition, the relevant intelligent technology research towards the cleaning system performance monitoring focuses only on the grain loss monitoring, without taking into account another important performance indicator-namely grain impurity ratio. Therefore, the performance of the grain impurity ratio monitoring device is an important factor to achieve adaptive control of the cleaning system, and a literature search found that there has not yet been seen a publication about this problem so far in China.